This invention relates to flow control devices for use with intravenous sets to control the rate at which fluids are passed from a container to a living subject.
A wide range of medications and nutrients are commonly administered intravenously. This is done by passing fluids containing the medication or the nutrient at a controlled rate via a needle or a cannula into a vein of a patient. Depending on the medication or nutrient being administered and the state of health of the patient, the flow rate at which fluids are infused may be critical. Furthermore, the total volume of fluid infused is typically also of interest.
In the past, two major approaches have been used to control the rate at which fluids are administered intravenously. The first approach is to use a conventional drip chamber which is manually controlled to adjust the drop rate through the drip chamber until the drops fall at a predetermined rate. This approach brings with it the advantage of simplicity in that only gravitational forces are needed to maintain the flow of fluids through the drip chamber.
However, manually controlled drip chambers are not satisfactory for all applications, for such drip chambers can permit fluid flow rate inaccuracies of as much as 30% above the requested flow rate or 60% below the requested flow rate. These inaccuracies are due to the fact that the size of individual drops passing through the drip chamber can vary as a function of the viscosity of the fluid being administered, the flow rate with which the fluid passes through the drip chamber, fluid pressure, and vibrational influences on the drip chamber. Furthermore, unless the drip chamber is carefully made to exacting tolerances, the drop volume may vary from one drip chamber to the next. This means that a drop rate appropriate for a preselected fluid flow rate with a first drip chamber is not necessarily appropriate for a second drip chamber, even if fluid viscosity and pressure are identical. Moreover, because of cold flow of tubing used in conjunction with conventional pinch clamps, a conventional, manually controlled drip chamber which is operating at a desired drop rate initially may well vary from this drop rate in time.
In an effort to provide greater accuracy of infusion rates, positive displacement infusion pumps have come into widespread use. Such pumps provide the advantage of accurately controlled infusion rates, largely independently of the pressure or the viscosity of the fluid being infused. However, such infusion pumps suffer from their own disadvantages. Because they typically operate at pressures of up to 60 psi, the danger of overpressure infusion is always present. Furthermore, infusion pumps tend to be relatively expensive, as well as heavy and cumbersome. In large part, the weight of infusion pumps is related to the size of the back up battery needed to power the pump in the event of a power failure. Because pumps operate motors on a regular basis, back up batteries for infusion pumps require large capacity. Furthermore, many infusion pumps bring with them problems related to the need to thread the IV set properly through the pump, and many infusion pumps require relatively expensive IV sets. Of course, when expensive IV sets are required for infusion pumps, it is less feasible to use the same intravenous set whether or not a pump is being used. This means that many hospitals are required to maintain stocks of two or more intravenous sets, and that a patient may well be subjected to the inconvenience of having an intravenous set replaced if the patient's physician determines that an infusion pump should be used.